1. Field of the Invention
The present invention relates to a balancer attachment for the spindle of a machining apparatus which is capable of compensating any imbalance caused by deviation of the center of gravity of the spindle when displacing and putting an associated cutting tool in a desired radial position.
2. Description of Prior Arts
In machining and shaping a piece of metal into a circular cross section the piece of metal is attached to the spindle end, and it is revolved at an increased speed to enable a stationary cutting tool to shape the workpiece into the cylindrical body. Assume that a part of workpiece which is not in cylindrical form is shaped into a circular cross section. Uneven distribution of the weight of the workpiece in the workspindle end will cause an appreciable imbalance and instability when the workpiece is revolved at an increased speed, thereby reducing the working precision and the durability of the workspindle. Particularly in case that a workpiece is large and heavy, there is a fear of allowing the workpiece to get off from the workspindle when revolving at an increased speed.
In an attempt to solve these problems it is proposed that a workpiece is fixed to the work bench of a machining apparatus and that a cutting tool, in turn, is fixed to the workspindle of the machining apparatus. FIG. 9 shows a representative example of machining apparatus of the type just described. Specifically workspindle 1 has a conical hollow 71 whereas cutting tool assembly E has conical projection 72. Conical projection 72 has a grooved end 73. It is inserted in conical hollow 71 of workspindle 1, and its grooved end 73 is caught by a collet (not shown). This arrangement has the advantageous effect of facilitating attachment of cutting tool assembly E to workspindle 1. The radial position of cutting tool assembly E must be controlled while machining. Necessary adjustment, however, must be made by stopping revolution of cutting tool assembly E and driving adjusting screw 75 to bring cutting tool 74 to a desired radial position. The fine adjustment, however, is very tedious, and requires skilfulness.
In the hope of eliminating such difficulties a tool attachment as shown in FIG. 10 is proposed. It comprises tool slide 7 on the end of hollow cylindrical spindle 1 of a machining apparatus, and a drive shaft (not shown) extending in spindle 1 and operatively connected to tool slide 7. Rotation of the drive shaft will cause cutting tool such as a single-point tool C to move across the end of workspindle 1 to a desired radial position. Advantageously the arrangement of FIG. 10 permits adjustment of tool radial position without stopping revolution of workspindle 1, accordingly improving the working efficiency. Deviation of the center of gravity of the rotating mass apart from the rotary axis of spindle 1 increases with displacement of slide 7 and tool C. Specifically when spindle 1 is revolved at the rate of 1000 revolutions per minute, a relatively large centrifugal force is generated in a direction from the central axis of spindle 1 to the center of gravity of slide 7, thereby reducing rotating and machining precision, and also reducing the durability of spindle 1. Therefore, the machining apparatus equipped with such tool attachment can be used only at a decreased speed.
In an attempt to reduce such imbalance caused by deviation of the center of gravity of the rotating mass rotary disk 2 is fixed to the end of spindle, and, as shown in FIG. 11, slide 7 is sandwiched between two rectangle weights 46 via rack and pinion 47. Each weight 46 is one half of slide 7 in weight. With this arrangement the shift of slide 7 in one direction will cause the shift of two weights 46 in the opposite direction. As a matter of fact, when slide 7 is displaced a given distance in one direction, two weights are shifted same distance in the opposite direction, and therefore, the size of whole unit is increased accordingly. Still disadvantageously, when slide 7 is being shifted in one direction, weights 46 are being shifted in the other direction, and as a matter of fact, this is likely to promote unnecessary displacement of slide 7 via racks and pinions 46. Accordingly the precision of displacement of slide 7 and associated tool, and hence machining precision will be lowered.